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On the execution of sequential function charts
The transition between the supervisory control theory (SCT) and its implementation in programmable logic controllers (PLCs) is not straightforward. This is mainly due to the fact that the SCT is stated in an event-based asynchronous setting whilst PLCs are signal-based, synchronous and sequential. Based on Petri nets, the PLC programming language sequential function chart (SFC) seems to be the ideal choice for this transition. However, the transition requires detailed knowledge of how the PLC and SFCs work. Different execution models for SFCs are presented and compared with the international standard IEC 61131-3. Often, the application of the SCT to a control problem results in a set of modules between which mutual exclusion and synchronisation are important aspects. The results indicate, however, that for modular SFC programs it seems generally impossible to simultaneously achieve both mutual exclusion between modules as well as synchronisation of modules without using workarounds that may be either manual or suffer from state space explosion. Nevertheless, one of the presented execution models, the immediate transit/immediate action model, together with a handshaking procedure is shown to give a simple solution to both mutual exclusion and synchronisation.
Implementation of a fuzzy-based level control using SCADA PLC模糊控制方法 This paper presents a SCADA (supervisory control and data acquisition) control via PLC (programmable logic controller) for a fluid level control system with fuzzy controller. For this purpose, a liquid level control set and PLC have been assembled together. The PLC used in this work has no fuzzy module or software. The required fuzzy program algorithms are written by the author. Sugeno type fuzzy algorithm has been used in this study. To achieve the parameters of the membership functions, MATLAB/Simulink program has been used. PLC has been programmed using achieved fuzzy algorithm. A SCADA system has been composed for monitoring of water level in tank and position of the actuator valve. The main objective of this work is to present an implementation setup has been realized with no fuzzy logic controller module/software in this study. The system described in this paper is a low cost solution that is intended for control purposes. Simulation and implementation results have been compared and similar results obtained with a good degree of accuracy.
A data flow-based structural testing technique for FBD programs
PLC的数据流结构化程序设计与开发测试
With increased use of programmable logic controllers (PLCs) in implementing critical systems, quality assurance became an important issue. Regulation requires structural testing be performed for safety-critical systems by identifying coverage criteria to be satisfied and accomplishment measured.
